Method for controlling an internal combustion engine

ABSTRACT

A common rail injection system for an internal combustion engine, wherein upon detection of a defective rail sensor system the transition from the normal operation to the emergency operation is determined reliably by means of a transition function. The transition function is determined beforehand from the characteristics of a system deviation as a function of time during normal operation. In so doing, the system deviation is calculated from a variance comparison of the rail pressure. The result of this defect transition process is a more noise-proof and more continuous transition from the normal operation to the emergency operation.

This application claims the priority of German patent document 101 57641.2, filed 24 Nov. 2001 (PCT International Patent Application No.PCT/EP02/12971, filed 20 Nov. 2002), the disclosure of which isexpressly incorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a process for controlling an internalcombustion engine with a common rail injection system.

In a common rail injection system the rail pressure is regulated. Theactual value of the rail pressure, thus the controlled variable, isgathered by an electronic controller by way of a rail pressure sensor.Said controller calculates the system deviation from a variancecomparison of the rail pressure and determines by way of a rail pressureregulator a select signal for a setting element, for example, a suctionthrottle or a pressure regulating valve. Since the rail pressurerepresents a significant parameter for the injection quality, one mustreact to a defective rail pressure sensor with appropriate measures. TheDE 199 16 100 A1 proposes in the case of a defective rail pressuresensor that one changes from normal operation to a start operation. Inthe start operation the rail pressure is controlled. In so doing, a highpressure pump is set to the maximum pump delivery rate; and a pressureregulating valve, which determines the outflow from the rail, is closed.The with this solution is the abrupt transition from the normal to thestart operation, as well as the resulting high rail pressure.

The U.S. Pat. No. 5,937,826 discloses an emergency operation (limp home)for an internal combustion engine with a defective rail pressure sensor.In the emergency operation the high pressure pump is controlled by wayof a characteristic diagram as a function of the engine speed and adesired rate of injection. The problem with this solution is thatimmediately after the transition into the emergency operation the railpressure can increase due to the previous large system deviation. Thus,the engine speed can increase. This undefined operating state remainsuntil the engine speed regulator reduces the desired rate of injectionand controls the rail pressure indirectly by way of the characteristicdiagram.

Therefore, the invention is based on the problem of making thetransition from the normal operation to the emergency operation safer.

The problem is solved by a process for controlling an internalcombustion engine during which a rail pressure is regulated in normaloperation, and upon detection of a defective rail pressure sensor thenormal operation is switched to an emergency operation the rail pressureis controlled in accordance with a transition function which smoothlyand reliably transitions rail pressure control from the normal operationto the emergency operation. Related embodiments are discussed further,below.

The invention provides that the transition from the normal operation tothe emergency operation is determined reliably by a transition function.In normal operation this transition function is determined beforehandfrom the characteristics of the system deviation of the rail pressure asa function of time. In addition, the system deviations in onemeasurement period or a specifiable number of system deviations can beconsidered. As one measure, at the end of the normal operation thetransition function defines a negative system deviation for the railpressure regulator in accordance with the measurement period, loggedduring the normal operation, or the number of system deviations. Analternative measure provides that a correcting volumetric flow of thecontrolled system is specified by means of the transition function. Thecorrecting volumetric flow is calculated from the difference between twosystem deviations. Both measures offer the advantage that a defined,continuous transition from the normal operation to the emergencyoperation takes place. The result of the direct impact of the transitionfunction on the rail pressure regulator or the controlled system is ashort reaction period after the rail pressure sensor fails.

At the end of the transition function a switch is made to thecharacteristic diagram, known from the prior art. A flanking measureprovides a loading characteristic diagram, with which the values of thecharacteristic diagram are additionally weighted. In addition, thecharacteristic diagram is corrected by limit lines, whereby the indirectdetermination of the rail pressure is aided by the engine speedregulator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a common rail injection system inaccordance with an embodiment of the present invention.

FIG. 2 is a schematic illustration of a common rail injection systemcontrol circuit in accordance with an embodiment of the presentinvention.

FIG. 3 is a schematic illustration of a common rail injection systemcontrol circuit in accordance with a further embodiment of the presentinvention.

FIGS. 4A, 4B are diagrams illustrating common rail injection systemoperation as an system emergency develops.

FIG. 5 is a timing diagram which depicts a transition function inaccordance with an embodiment of the present invention.

FIG. 6 is a characteristic diagram to determine leakage-volumetric flowin accordance with an embodiment of the present invention.

FIG. 7 is a loading characteristic diagram in accordance with anembodiment of the present invention.

FIG. 8 is a diagram illustrating implementation of an upper flow limitin accordance with an embodiment of the present invention.

FIG. 9 is a characteristic diagram for determining leakage-volumetricflow in accordance with an embodiment of the present invention.

FIG. 10 is a program flowchart illustrating a common rail injectionsystem control in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a block diagram of an internal combustion engine 1 with acommon rail injection system. The common rail injection system comprisesa first pump 4, a suction throttle 5, a second pump 6, a high pressureaccumulator and injectors 8. In the text below the high pressureaccumulator is referred to as the rail 7. The first pump 4 delivers thefuel from a fuel tank 3 to the suction throttle 5. The pressure levelafter the first pump 4 is, for example, 3 bar. The volumetric flow tothe second pump 6 is determined by way of the suction throttle 5. Thesecond pump 6 in turn delivers the fuel under high pressure into therail 7. In diesel engines the pressure level in the rail 7 is more than1,200 bar. The injectors 8 are connected to the rail 7. The fuel isinjected by means of the injectors 8 into the combustion chambers of theinternal combustion engine 1.

The internal combustion engine 1 is controlled and regulated by means ofan electronic device controller 11 (ED C). The electronic devicecontroller 11 contains the customary components of a microcomputersystem, for example, a microprocessor, I/O modules, buffer and memorymodules (EEPROM, RAM). The operating data in the characteristicdiagrams/characteristic lines that are relevant for operating theinternal combustion engine 1 are entered into the memory components.With said data the electronic device controller 11 calculates theoutputs from the inputs. In FIG. 1 the following inputs are shown as anexample: a rail pressure-actual value pCR(IST), which is measured bymeans of the rail pressure sensor 10; the speed nMOT of the internalcombustion engine 1; a performance request FW; an internal cylinderpressure pIN, which is measured by means of the pressure sensors 9; andan input E. Under the input E there are subsumed, for example, thecharge air pressure pLL of the turbocharger 2 and the temperatures ofthe coolant and lubricant. FIG. 1 shows a signal ADV, for controllingthe suction throttle 5, and an output A as the outputs of the electronicdevice controller 11. The output A stands for the other actuatingsignals for controlling and regulating the internal combustion engine 1,for example, the injection start BOl and the rate of injection ve.

In practice the select signal ADV is designed as a PWM signal (pulsewidth modulated), by means of which a corresponding current value forthe suction throttle 5 is set. When the current value is zero (i=0), thesuction throttle 5 is fully opened, i.e. the volumetric flow, deliveredby the first pump 4, flows unimpeded to the second pump 6.

FIG. 2 shows a control circuit in a first design. It contains as the keyelements a first summation point 16, a rail pressure regulator 13, aconversion 17 and the rail 7. The conversion 17 contains the conversionof the desired volumetric flow V(SOLL) into the select signal ADV, thesuction throttle 5 and the second pump 6. Inputs E, for example the fueladmission pressure, the operating voltage and the engine speed, are fedto the conversion 17. The conversion 17 and the rail 7 correspond to thecontrolled system. This basic control circuit is supplemented with afirst switch 12, a second switch 15 and a second summation point 18.FIG. 2 shows the first switch 12 and the second switch 15 in theirswitch position in accordance with the normal operation of the internalcombustion engine (continuous line). In normal operation the railpressure-actual value pCR(IST) at the first summation point 16 iscompared, as the controlled variable, with the reference variable, therail pressure-desired value pCR(SW), and fed as the system deviation dRto the rail pressure regulator 13. As a function of the system deviationdR, the rail pressure regulator 13 determines a regulator-volumetricflow VR. At the second summation point 18 a consumption-volumetric flowV(VER) is added to the former regulator-volumetric flow. Theconsumption-volumetric flow V(VER) is calculated as a function of theengine speed nMOT and a desired rate of injection Q(SW). The result ofthese two volumetric flows is the desired volumetric flow V(SOLL), asthe manipulated variable, which represents the input for the conversion17. By means of the conversion 17 the select signal ADV for the suctionthrottle 5 is generated, which then results in an actual volumetric flowV(IST) by way of the second pump 6.

Upon detection of a defective rail pressure sensor, the first switch 12changes into the switch position, shown as a dashed line. In this switchposition the system deviation is specified by means of the transitionfunction ÜF. The transition function was determined beforehand duringnormal operation from the characteristics of the system deviations dR asa function of time. In practice, the system deviations in onemeasurement period are also considered.

As an alternative, even just a specifiable number of system deviationscan be used, of course. At the end of the normal operation, thetransition function ÜF defines the system deviation for the railpressure regulator 13 according to the measurement period, logged duringthe normal operation. Following the passage of this time stage, thetransition function ÜF ends, and the second switch 15 changes into theposition, shown as a dashed line. The desired volumetric flow V(SOLL) isnow calculated from the consumption-volumetric flow V(VER) and aleakage-volumetric flow V(LKG). This in turn is defined reliably by thecharacteristic diagram 14 as a function of the engine speed nMOT and thedesired rate of injection Q(SW).

FIG. 3 depicts the control circuit in a second embodiment. Thedistinction between the control circuit of FIG. 2 and that of FIG. 3 isa DT1 block 19, a third switch 20 and the omission of the first switch12. The second switch 15 and the third switch 20 are shown for thenormal operation (continuous line). The function of the control circuitin normal operation is in conformity with the description in FIG. 2.Upon detection of a defective rail pressure sensor, the second switch 15and the third switch 20 change into the dashed position. The railpressure regulator 13 is immediately deactivated. At this stage thedesired volumetric flow V(SOLL) is computed through addition from theleakage-volumetric flow V(LKG), the consumption-volumetric flow V(VER)and the correcting volumetric flow V(KORR). The correcting volumetricflow V(KORR) is determined by means of the DT1 block 19 from thetransition function ÜF. This is calculated from the difference betweentwo system deviations in normal operation and specified to the DT1 block19 as the negated step function. The transition function ÜF is explainedin detail in connection with FIG. 4B. If the output of the DT1 block 19falls below the threshold value or a time stage expires, the transitionfunction is deactivated. Then the third switch 20 returns into itsstarting position (normal operation). In the end the desired volumetricflow V(SOLL) is defined only by the characteristic diagram 14 and theconsumption-volumetric flow V(VER).

FIG. 4 consists of the partial FIGS. 4A and 4B. In addition, for thenormal operation over time FIG. 4A shows the pressure curve of the railpressure-actual value pCR(IST) and the rail pressure-desired valuepCR(SW), and FIG. 4B shows the resulting system deviation dR. At time t1the rail pressure-actual value PCR(IST) is equivalent to the railpressure-desired value pCR(SW), corresponding to point A. The followingobservation assumes that the rail pressure-desired value pCR(SW) remainsunchanged for the period of observation. At time t1 the system deviationis zero, corresponding to point D of FIG. 4B. After time t1, the railpressure-actual value pCR(IST) begins to decrease. The cause is thedefective rail pressure sensor 10. At time t3 there is already a systemdeviation dR3 at point B. At time t5 the defect is detected at point C.The result of the two curves in FIG. 4A is for the measurement period dtin FIG. 4B a system deviation dR in conformity with the curve withpoints D, B and E.

The process, according to the control circuit in FIG. 2, continues asfollows. Upon detection of the defective rail pressure sensor at timet5, the transition function ÜF is activated. This is illustrated in FIG.5. The transition function ÜF corresponds to the negated systemdeviations dR. Starting from time t6, this is specified to the railpressure regulator 13 for the same period of time as the measurementperiod dt, curves F and G. For example, the system deviation dR3,measured at time t3 at point B, is specified as dR3 at time t8. Startingfrom time t10, the transition function ÜF is deactivated in that thesecond switch 15 changes its switch position. Instead of the measurementperiod dt, a specifiable number of system deviations can also be used.

When the control circuit according to FIG. 3 is used, the processproceeds as follows. Upon detection of the defective rail pressuresensor at time t5, the system deviation at time t5, equivalent to thevalue of point E, is subtracted from the system deviation at time t1,equivalent to the value of point D. This difference DIFF is depicted inFIG. 4B. The transition function ÜF corresponds to the negateddifference DIFF. This is fed as the step function to the DT1 block 19.The correcting volumetric flow V(KORR) is calculated by means of the DT1block. Following passage of a specified time span or upon dropping belowa threshold value, the DT1 block 19 is switched off by returning theswitch 20 from the switch position, indicated by the dashed line, intothe switch position, indicated by the continuous line.

Both methods offer the advantage that impermissible changes in the railpressure due to a defective rail pressure sensor can be significantlydecreased. The rail pressure changes in the case of a defective sensorbecause the high pressure control circuit continues to process thedefective sensor signal until detection of the sensor defect andcalculates from that the actuating signal for the suction throttle.

FIG. 6 depicts a characteristic diagram 14 for determining theleakage-volumetric flow V(LKG). The engine speed nMOT is plotted on theabscissa. A desired rate of injection Q(SW) is plotted as the secondinput on the ordinate. The Z axis corresponds to the leakage-volumetricflow V(LKG). A specifiable operating area is assigned to each supportingpoint in this characteristic diagram. The operating areas are shaded inFIG. 6. One such operating area is defined by the variables dn and dQ.Typical values are, for example, 100 revolutions and 50 cubicmillimeters per stroke. In FIG. 6 a supporting point A is sketched in asan example. This supporting point A is derived from the two inputvalues—n(A) equals 3,000 revolutions per minute and Q(A) equals 40 cubicmillimeters per stroke. A leakage-volumetric flow V(LKG) of, e.g., 7.2liters per minute is assigned as the Z value to the supporting point A.Then the leakage-volumetric flow V(LKG), determined by means of thecharacteristic diagram 14, is weighted by means of a loadingcharacteristic diagram, which is shown in FIG. 7. For the previousexample, the result for the supporting point A, for example, is aloading factor of 0.95. Thus, in the end the leakage-volumetric flowV(LKG) is calculated at 6.84 liters per minute.

The Z values of the characteristic diagram 14 are determined in normaloperation only when the common rail injection system is in a steadystate, for example at operating point n(A) and Q(A). In this respect theregulator-volumetric flow VR or the filtered value is assigned to thecorresponding operating area of the characteristic diagram 14 and storedas the Z value. The stored values represent a measure for the leakage ofthe common rail injection system. To calculate the Z values of thecharacteristic diagram 14, the integrating content of the rail pressureregulator 13 can be used, instead of the regulator-volumetric flow VR.It is clear that the Z values can already be permanently applied evenupon delivery of the internal combustion engine. The Z values can becorrected by means of the loading characteristic diagram of FIG. 7.Thus, an inadmissibly high increase or decrease in the rail pressurefollowing the failure of the rail pressure sensor, caused by too largeor too small stored values of the characteristic diagram 14, can beeffectively prevented.

The characteristic diagram 14, shown in FIG. 6, has 5 times 4 supportingpoints. The advantage of this lies in a good overview and that fewermemory locations are required. The problem here lies in the circumstancethat smaller values of the desired rate of injection Q(SW) below Q(A)cannot be represented. The desired rate of injection Q(A) is equivalent,for example, to a value of 40 cubic millimeters per stroke. If at thisstage the speed regulator calculates a smaller value of the desired rateof injection Q(SW), for example, 18 cubic millimeters per stroke, thenthe supporting point Q(A) is used in the characteristic diagram 14. Thistoo large value of the characteristic diagram 14 leads to an increase inthe rail pressure during the emergency operation and thus to higherstress on the crankshaft. When using a characteristic diagram 14 withfew supporting points, this problem can be remedied to some degree byintroducing a limit line. In the area of the desired rate of injectionvalues that are smaller than the smallest desired rate of injectionvalues in the stationary state, the leakage-volumetric flow V(LKG) ofthe characteristic diagram 14 is decreased linearly by means of thelimit line. Such a limit line GW is depicted in FIG. 8.

The desired rate of injection Q(SW) is plotted on the abscissa. Theleakage-volumetric flow V(LKG) is plotted as the output on the ordinate.The limit line GW applies to a stationary engine speed, for example, forthe supporting point A from FIG. 6, where n(A) equals 3,000 revolutionsper minute. A leakage-volumetric flow of 7.2 liters per minutes isequivalent to a value Q(A) of 40 cubic millimeters per stroke. A desiredrate of injection Q(SW) of 18 cubic millimeters per stroke, calculatedby the speed regulator, works out to a corresponding leakage-volumetricflow of 1.9 liters per minute. Thus, the leakage-volumetric flow V(LKG),calculated by means of the characteristic diagram 14, can be correctedby means of the limit line GW when the desired rate of injection Q(SW)drops to smaller values. In this manner the increase in the railpressure is limited when the rail pressure sensor fails. Hence, a morestable working point develops faster.

To prevent an impermissible increase in the rail pressure duringemergency operation, the characteristic diagram 14 can also exhibit moresupporting points. Should the rail pressure increase following thefailure of the rail pressure sensor, the engine speed also increases. Asa secondary reaction, the speed regulator reduces the desired rate ofinjection Q(SW). Hence, the leakage-volumetric flow V(LKG) is determinedfrom the characteristic diagram 14 for ever decreasing desired rate ofinjection values Q(SW). An increase in the rail pressure duringemergency operation can be effectively prevented, when thecharacteristic diagram 14 in the area of the desired rate of injectionvalues, which are smaller than the smallest desired rate of injectionvalues in the stationary state, is allocated small leakage-volumetricflows (Z values), ideally the value zero liters per minute. The railpressure is prevented from increasing too fast, since the desiredvolumetric flow V(SOLL) is decreased as the rail pressure increases. Inparticular, in the light load area of the internal combustion engine,the increase in the rail pressure is limited early. FIG. 9 shows asection of such a designed characteristic diagram 14. In operationsmaller leakage-volumetric flows (Z values) are assigned in conformitywith the smaller desired rate of injection values Q(SW). Then theleakage-volumetric flow V(LKG), calculated herewith, is weighted bymeans of the loading characteristic diagram of FIG. 7.

FIG. 10 shows a program flowchart of the process. It begins at step S1after initialization of the electronic device controller. At S2 thestart operation for the internal combustion engine is activated. Then itis checked whether the start operation has ended. In practice the startoperation has ended when the rail pressure-actual value pCR(IST) exceedsa limit value (regulator release pressure); and/or the engine speed nMOTexceeds a limit value (regulator release speed). If the start operationhas not ended yet, the program cycles through the wait loop at S4. Afterthe start operation has ended, the control of the rail pressure pCR isactivated at S5. Then the system deviation dR over time is logged andstored at S6. Thus, the system deviations dR of a measurement period dtor a specifiable number of values can be selected hereby. At S7 it ischecked whether the values, delivered by the rail pressure sensor, areerror-free. If the rail pressure sensor is flawless, the normaloperation is maintained—step S8, and the program flowchart continues atS5. If the test at S7 shows that the signals of the rail pressure sensorare defective, the emergency operation and the transition function ÜFare activated—step S9 and S10. The stored system deviation is specifiedinversely by means of the transition function ÜF to the rail pressuresensor; or a correcting volumetric flow is determined from thedifference between two system deviations. Then it is checked at S11whether the measurement period dt has expired. As an alternative,instead of the time (dt), the query of a number (n) of system deviationscan be carried out.

If the query is negative at S11, the program cycles through a wait loopat step S12. If the test results at S11 are positive, the transitionfunction is ended—step 13. During an emergency operation, the railpressure is determined indirectly by the speed regulator by means of thecharacteristic diagram 14. As another measure, the operator of theinternal combustion engine is informed about the emergency operation,for example, by means of a corresponding warning light and a diagnosticentry.

1. A method for controlling an internal combustion engine with a commonrail injection system, comprising the acts of: regulating a railpressure during a normal operation; determining whether a rail pressuresensor is defective; switching, upon determining the rail pressuresensor is defective, from normal operation to an emergency operation,wherein the switching from the normal operation to the emergencyoperation is controlled in accordance with a transition function;calculating system deviations during normal operation from a variancecomparison of a rail pressure-actual value with a rail pressure-desiredvalue; and determining the transition function from at least one of thesystem deviations.
 2. The method of claim 1, wherein the transitionfunction is determined from one of the system deviations of ameasurement period and a predetermined number of system deviations. 3.The method of claim 2, wherein the transition function corresponds tothe calculated system deviations with opposite sign.
 4. The method ofclaim 3, further comprising the act of: when switching from normaloperation to emergency operation, calculating a regulator volumetricflow as a function of the transition function.
 5. The method of claim 4,wherein the transition function ends upon completion of one of themeasurement period and the predetermined number of system deviations. 6.The method of claim 2, wherein the transition function is determinedfrom a difference between a first system deviation and a second systemdeviation.
 7. The method of claim 6, wherein the transition functioncorresponds to the calculated system deviations with opposite sign. 8.The method of claim 7, further comprising the act of: when switchingfrom normal operation to emergency operation, calculating a regulatorvolumetric flow as a function of the transition function.
 9. The methodof claim 8, wherein the transition function ends upon completion of oneof the measurement period and the predetermined number of systemdeviations.
 10. The method of claim 3, further comprising the act of:calculating, when switching from normal operation to emergencyoperation, a desired volumetric flow as a function of a regulatorvolumetric flow and a consumption-volumetric flow; and regulating railpressure as a function of the desired volumetric flow.
 11. The method ofclaim 6, further comprising the act of: calculating, when switching fromnormal operation to emergency operation, a desired volumetric flow as afunction of a regulator volumetric flow and a consumption-volumetricflow; and regulating rail pressure as a function of the desiredvolumetric flow.
 12. The method of claim 11, wherein, in the act ofcalculating the desired volumetric flow, a leakage-volumetric flow,determined from a characteristic diagram, is also considered incalculating the desired volumetric flow.
 13. The method of claim 10,wherein, when the transition function has ended, the desired volumetricflow is calculated as a function of the consumption-volumetric flow anda leakage-volumetric flow.
 14. The method of claim 11, wherein, when thetransition function has ended, the desired volumetric flow is calculatedfrom the consumption-volumetric flow and the leakage-volumetric flow.15. The method of claim 10, wherein the consumption-volumetric flow iscalculated as a function of an engine speed and a desired rate ofinjection.
 16. The method of claim 11, wherein theconsumption-volumetric flow is calculated as a function of an enginespeed and a desired rate of injection.
 17. The method of claim 13,wherein the values of the leakage-volumetric flow in the characteristicdiagram are determined in normal operation, and the value of theregulator volumetric flow is set as corresponding to theleakage-volumetric flow when operating in a steady state.
 18. The methodof claim 14, wherein the values of the leakage-volumetric flow in thecharacteristic diagram are determined in normal operation, and the valueof the regulator volumetric flow is set as corresponding to theleakage-volumetric flow when operating in a steady state.
 19. The methodof claim 17, wherein the regulator-volumetric flow value is filtered.20. The method of claim 13, wherein the regulator-volumetric flow valueis filtered.
 21. The method of claim 13, wherein the values of theleakage-volumetric flow in the characteristic diagram are determined innormal operation, and an integrating content of the rail pressureregulator is set as corresponding to the leakage-volumetric flow whenoperating in a steady state.
 22. The method of claim 14, wherein thevalues of the leakage-volumetric flow in the characteristic diagram aredetermined in normal operation, and an integrating content of the railpressure regulator is set as corresponding to the leakage-volumetricflow when operating in a steady state.
 23. The method of claim 15,wherein the leakage-volumetric flow is corrected to smaller valuesdefined by limit lines as the desired rate of injection decreases. 24.The method of claim 16, wherein the leakage-volumetric flow is correctedto smaller values defined by limit lines as the desired rate ofinjection decreases.
 25. The method of claim 23, wherein theleakage-volumetric flow is weighted by a loading characteristic diagram.26. The method of claim 24, wherein the leakage-volumetric flow isweighted by a loading characteristic diagram.
 27. A system forcontrolling an internal combustion engine with a common rail injectionsystem, comprising: means for regulating a rail pressure during a normaloperation; means for determining whether a rail pressure sensor isdefective; means for switching, upon determining the rail pressuresensor is defective, from normal operation to an emergency operation,wherein the switching from the normal operation to the emergencyoperation is controlled in accordance with a transition function; meansfor calculating system deviations during normal operation from avariance comparison of a rail pressure-actual value with a railpressure-desired value; and means for determining the transitionfunction from at least one of the system deviations.
 28. A system forcontrolling an internal combustion engine with a common rail injectionsystem, comprising: a rail pressure regulator; a rail pressure sensor;and a controller, the controller controlling the rail pressure regulatorto control rail pressure in at least a normal operation and an emergencyoperation, wherein upon a determination that the rail pressure sensor isdefective, the controller switches rail pressure control from normaloperation to emergency operation in accordance with a transitionfunctions calculating system deviations during normal operation from avariance comparison of a rail pressure-actual value with a railpressure-desired value; and determining the transition function from atleast one of the system deviations.
 29. The system of claim 28, whereinthe controller determines whether the rail pressure sensor is defective.